This invention relates to the field of meander line loaded antennas and, in particular, to methods for tuning the same.
It is well known in the art that antenna performance is dependent upon the relationship between antenna length and the wavelength of the desired frequency of operation. This relationship determines the operating mode of the antenna, which modes are labeled as fractional parts of the wavelength. It is further known that the electrical length of an antenna may be considerably changed by the series connection of a coil therewith.
The proliferation of wireless communication devices drives a constant physical need for smaller, less obtrusive, and more efficient antennas. U.S. Pat. No. 5,790,080, issued to Apostolos, addresses this need, disclosing an antenna design with improved efficiency in terms of size or form factor versus electrical performance. An antenna is provided comprising: one or more conductive elements for acting as radiating antenna elements, and a slow wave meander line means adapted to couple electrical signals between the conductive elements, wherein the meander line means has an effective electrical length which affects the electrical length and operating characteristics of the antenna.
The antenna includes sequential low and higher impedance sections interconnected by substantially orthogonal sections, and by diagonal sections. This arrangement allows the construction of shorting switches between the adjacent low and higher impedance sections to provide for electronically switchable control of the length of the meander line and thus the center frequency of the attached antenna. These switches may take any suitable form, such as mechanical switches or electronically controllable switches such as pin diodes.
Essentially this design relies on discrete switch elements to short out sections of the meander line tuning module. The frequency of operation is thus changed by changing the net time delay through the module. A multiplicity of switches and their attending complex control circuitry is needed to tune the meander line antenna. Therefore, what is needed is a more efficient way to tune a meander line antenna. A method of tuning involving adjusting only one voltage is also needed.
The present invention offers an alternative method of tuning a meander line antenna. A layer of PN semiconductor material is inserted between a ground plane and a base element. A dc voltage is applied between the ground plane and the base element. A change in capacitance between the ground plane and the base element is effected. The impedance of the base element is thus changed, resulting in a change in the delay through the meander line tuning module as the propagation constant. This change in delay tunes the meander line antenna in the same manner as discrete switch elements by adjusting only a single voltage.
Therefore, it is an aspect of this invention to provide a more efficient and robust means of tuning a meander line antenna.
It is another aspect of the invention to provide a method for tuning a meander line antenna that does not rely on a multiplicity of discrete switch elements.
It is a further aspect of the invention to provide a method for tuning a meander line antenna that relies on tuning a single voltage.
These aspects of the invention are not meant to be exclusive and other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the appended claims and accompanying drawings.